The present invention relates to a varnish coater disposed between a printing unit and a delivery apparatus of a rotary press or in an independent coating unit to apply varnish on a printed surface.
The surface of paper printed by a rotary printing press is not quickly dried and can be contaminated in the subsequent processing. In a sheet-fed rotary printing press, offsetting tends to be caused when printed sheets are stacked. In order to solve these problems, conventionally, a dryer is arranged in a delivery path of the printed products, or a powder is sprayed on the printed paper surfaces. However, in this case, the dryer becomes 1arge, and powder spraying results in surface roughening of the printed surface. Surface roughening tends to entail a loss of gloss and subsequent poor printing. Instead of these techniques, varnish is applied to the printed surface to prevent the surface from being contaminated and to give it gloss. Varnishing is performed in printed products such as covers of books, catalogs and pamphlets which require an aesthetic effect.
The varnish coater is used as an independent apparatus. However, recently, the varnish coater is generally disposed in a delivery path of a printing press to shorten a coating time and an associated operation time for restacking the printed sheets and hence to improve the coating efficiency. The varnish coater generally has rollers in the same manner as that of a dampening apparatus for dampening a surface of a plate mounted on a plate cylinder of the printing unit. Varnish stored in a varnish pan is supplied to a surface of a blanket cylinder through the rollers. The varnish is transferred to a sheet passing between the blanket cylinder and an impression cylinder.
However, in the conventional varnish coater of this type, there arise problems in respect to a rotation transmission mechanism of each roller and a nonuniform thickness of a varnish film caused thereby. The printing press is stopped when the sheets are restacked, or a stack board is replaced, or an underlay for a blanket of the blanket cylinder is adjusted due to a change in paper size. In such a case, the blanket cylinder is separated from the impression cylinder, while the rollers used for applying varnish continue to rotate to prevent varnish from hardening before the restart time.
It is occasionally required that the blanket cylinder be driven from the drive line side of the press, and that the rollers consisting of a pan roller (upsteam roller), a metering roller and a form roller be driven by another variable motor so as to adjust the thickness of a varnish film. When the above operation is performed, however irregular rotation occurs between the blanket cylinder and the form roller which are driven by the different drive sources, thus resulting in an irregular thickness of the varnish film. However, when the form roller is coupled to the blanket cylinder through a gear, the form roller must be stopped when the blanket cylinder is stopped for cleaning and adjustment of the underlay of the blanket. As a result, the varnish on the outer surface of the form roller is hardened, and the form roller must also be cleaned, resulting in inconvenience.